KINETICS, ISOTHERMS, AND COMPETITION IN POLYMER ADSORPTION USING THE QUARTZ-CRYSTAL MICROBALANCE

The kinetics and isotherms of adsorption of polystyrene and poly(ethylene oxide) at the solution/metal interface have been measured in situ using the quartz crystal microbalance. For polystyrene, cyclohexane at the theta temperature was used as the solvent and gold as the surface. Isotherms for polystyrene over the molecular weight range 10(4) to 10(5) were confirmed to be of the high-affinity type. The effect of solution viscosity on frequency measurements was considered in detail and shown to be negligible over a range of conditions. The surface displacement of lower molecular weight polymer by higher molecular weight polymer was shown to be rapid. Using polymers having a wide molecular weight distribution, it was demonstrated that a limiting, stable value for surface coverage is attained more slowly, suggesting continuous competition for sites among molecules of different sizes. Poly(ethylene oxide) adsorbed onto gold from a good solvent, whereas polystyrene did not.